This invention relates to a touch panel, and particularly relates to a touch panel that has two resistance members facing each other with a certain space in between and that detects a touched position by measuring resistence between each standard point of the two resistance members and a contact point.
Recently, personal digital assistants (PDA), sub-notebook personal computers, and the like have been used as portable data terminals. For such data terminals, portability and ease of use are taken into account. In general, as an input device of such a data terminal, a resistence-member touch panel is set on a display device such as a liquid crystal display. Input operations in the data terminal are executed by touching the surface of the resistance-member touch panel by a finger or pen. The touched position is detected as X-Y coordinates.
The resistance-member touch panel has a touch substrate that is used in input operations and a display substrate. The touch substrate is made of polyethylene terephthalate, polycarbonate, or poly methacrylate resin that is transparent. For protection, a light-hardening acrylate resin film is formed on either or both of surfaces of the resin. The display substrate is made of soda-lime glass or tempered glass. The surface of each substrate, that is facing the other substrate, is covered by a thin layer of indium/tin oxide (referred to as xe2x80x9cITOxe2x80x9d hereinafter) as a transparent conductive layer.
The touch panel requires high transparency in a visible-light region and, especially the transmittance of light with a wavelength of 550 nm or so needs to be high. To achieve the high transparency for the touch panel, an appropriate metal oxide can be inserted between the conductive substrate (in this case, the touch substrate or display substrate) and the transparent conductive layer, according to an well-known technique. Hereinafter, the inserted metal oxide is referred to as the xe2x80x9cundercoat layer.xe2x80x9d The technique is specifically explained. A metal oxide layer of silicon dioxide (SiO2) or of silicon dioxide/tin oxide base (SnSiOx, for example) is formed between each substrate and the corresponding transparent conductive layer. In this case, the conductive layer, the metal oxide layer, and the film are formed so that their refractive indexes becomes high-low-high or low-high-low in this alternate order in the arrangement. By means of this alternation, the transparency of the touch panel is improved. In general, the light reflectivity is high in areas of the touch panel that are in contact with air, and this is the main factor that decreases the light transmittance. On this account, the technique has a profound significance although it is not further explained in detail in this specification.
As stated above, the transparent conductive substrate is composed of: a substrate that is made of polyethylene tetephthalate, polycarbonate, poly methacrylate resin or glass; an undercoat layer that is made of an insulating metal oxide, such as SiO2, and is directly formed on the substrate; and a transparent conductive layer formed on the undercoat layer. In this construction, a contact level (or, a degree of adhesion) is low between the substrate and the undercoat layer. As such, after the transparent conductive substrate has been left under high temperature and high humidity for long hours or when it comes in contact with any kind of alcohol or alkaline solution, the transparent conductive layer easily comes off the substrate. In this way, the transparent conductive substrate is poor in environment resistance and solution resistance.
When pressure is given to the touch panel through an input operation, a liquid crystal layer of the liquid crystal display directly receives the pressure. This may cause jitter on the liquid crystal layer and so may impair the display function. To avoid this problem, a bond layer is provided on a non-display area (an outer region) of the liquid crystal display, and the touch panel is fixed to the liquid crystal display via this bond layer. By the medium of the bond layer, there would be a space between the touch panel and the liquid crystal display. As such, it should be obvious that the display substrate definitely requires an appropriate rigidity against the pressure.
The following are mainly required as characteristics of the touch panel that is provided for a portable data terminal.
(1) high transparency
(2) high resistance against mechanical impact and friction caused when the touch panel is touched in an input operation
(3) high suitability for reduction in thickness and weight
(4) high impact-resistance (so that the substrate and the like will not be broken when the data terminal is dropped)
(5) wide operating temperature
(6) appropriate rigidity
The characteristics described in (1) and (2) can be achieved at the practically required level through: improvements to the technique of forming a transparent conductive layer on the touch substrate made of polyethylene terephthalate and on the display substrate made of glass; insertion of appropriate inorganic metal oxide or resin layer between the touch substrate and the transparent conductive layer; and formation of an appropriate resin layer onto the surface of the touch substrate (this resin layer is referred to as the xe2x80x9chard coat layerxe2x80x9d hereinafter).
As to the characteristics described in (3) and (4), the reduction in thickness and weight is limited when only conventional techniques are used. As one example, suppose that glass is used for the display substrate. In this case, even if tempered glass instead of typical soda glass is used, a metal frame for impact absorbency or a transparent resin sheet as a reinforcing material needs to be attached to the surface of the tempered glass. As long as glass is used, it may be impossible to keep the glass from being broken when a strong mechanical impact is given.
To address this problem, it has been suggested that the glass should be replaced with a transparent resin film, such as polycarbonate or polymethyl methacrylate, that is relatively thin and has a proper rigidity.
There are roughly two ways to construct the display substrate when the transparent conductive layer such as ITO is formed on the transparent resin film replacing the glass substrate.
One way is to form the transparent conductive layer directly onto one side of the transparent resin film. Note that the transparent resin film in this example serves as a supporting member formed from material, such as polycarbonate or polymethyl methacrylate. This construction is referred to as the xe2x80x9csingle-piece constructionxe2x80x9d that includes the transparent conductive layer and the supporting member.
The other way is achieved by the construction that is referred to as the xe2x80x9cmultilayer constructionxe2x80x9d hereinafter. As described above, the transparent resin film is made up of polycarbonate or polymethyl methacrylate whose one side is covered by the transparent conductive layer. In this multilayer construction, a transparent resin sheet, such as polycarbonate or. polymethyl methacrylate, covers the non-conductive surface of the transparent conductive resin, with an acrylic base bond layer being set in between. The transparent resin sheet serves as a supporting member to give the rigidity to the display substrate. Thus, the multilayer construction of the display substrate includes, from above, the transparent conductive layer, transparent resin film, bond layer, and supporting member.
In the case of the single-piece construction, an organo-siloxane layer that has a bridging construction is inserted between the supporting member and the transparent conductive layer such as ITO. By doing so, a transparent conductive resin film is realized, which has: durability that is practically required to withstand friction caused from input operations; high adhesion with the transparent conductive layer; transparency; proper rigidity; and heat resistance.
In general, transparent conductive layers are formed according to the vacuum film-thinning technique, such as the sputtering method, resistance evaporating method, and electronic-beam evaporating method. When a transparent conductive layer is formed on polycarbonate with about 0.4% of saturated water content or on polymethyl methacrylate with about 2.0% of saturated water content, a dehydrating process definitely needs to be performed on the substrate before a film is formed on the substrate. If the dehydrating process is not adequately performed, stability in heat resistance of the transparent conductive layer and adhesion between the transparent conductive layer and the substrate are considerably deteriorated.
Thus, the following problem has been pointed out. That is, as compared with a case where glass is used, it takes a longer period of time to finish the dehydrating process in a vacuum when a film is formed in the single-piece construction. This is because, in the single-piece construction, a transparent conductive layer is directly formed on a relatively thick supporting member that has a proper rigidity. In the case of the multilayer construction, meanwhile, the transparent conductive layer is formed on the film of polycarbonate or polymethyl methacrylate that is thinner than the supporting member. Therefore, the dehydrating process can be finished in a shorter period of time, and so mass-productivity can be increased. In addition, this construction is not so complicated. These are the reasons why the multilayer construction has been employed more widely than the single-piece construction.
However, in the case of the multilayer construction, there would be a great difference between linear expansion coefficients of the supporting member and the transparent resin film, depending on a combination of the used materials. The linear expansion coefficients are shown below corresponding to the materials.
Polycarbonate: xcx9c6.2xc3x9710xe2x88x925/xc2x0 C.
Polymethyl methacrylate: xcx9c6.9xc3x9710xe2x88x925/xc2x0 C.
Polyethylene terephthalate: xcx9c1.5xc3x9710xe2x88x925/xc2x0 C.
Because of the difference, the display substrate may be deformed in consequence of changes in environmental conditions, such as temperature and humidity.
For example, when polyethylene terephthalate is used for the transparent resin film, the following problem occurs due to the low glass transition point (about 70xc2x0 C.). If the touch panel is left in an area exposed to a temperature exceeding 70xc2x0 C., the transparent resin film will shrink greatly as compared with the supporting member. This results in a low heat-resistance because of deformation, such as corrugation, of the display substrate.
The problem caused by the change in temperature is more remarkable when polyethylene terephthalate is used for the touch substrate. Specifically, a malfunction occurs when an input operation is performed. A further problem is that failures occur to electrical contacts of a panel side connector that connects the touch panel body with a control substrate.
Accordingly, the operating temperature of the touch panel is limited to approximately from 0xc2x0 C. to 40xc2x0 C. when polyethylene terephthalate is used for the transparent resin film of the touch substrate or the display substrate.
The deformation caused by the corrugation can be reduced by using material that can minimize a difference in the linear expansion coefficients of each layer comprising the touch panel and the supporting member. As one example, the heat-resistance can be ensured by using polycarbonate whose glass transition point is high (150xc2x0 C.).
Yet, surface hardness of polycarbonate is low. Thus, it is absolutely necessary to coat both sides of each layer with a transparent resin layer of silicon, cellulose, melamine, urethane, or the like as a protection. Here, the alkali resistance and solution resistance of polycarbonate are low as compared with polyethylene terephthalate. For this reason, there would still be problems. Specifically, a contact level between polycarbonate and the hard coating layer is easy to deteriorate in a wet etching process. The wet etching process is performed for forming a transparent conductive layer such as ITO on the hard coating layer which is absolutely necessary in manufacturing a touch panel. Moreover, although conductive wiring is formed on the transparent conductive layer using mixture ink of carbon and silver ink or silver according to a paint printing method, contact resistance between the conductive wiring and the transparent conductive layer is subject to fluctuation under a high temperature and high humidity.
It is therefore a primary object of the present invention to provide a touch panel which has an excellent contact level between a undercoat layer and a substrate on which the undercoat layer is formed.
It is a secondary object of the present invention to provide a touch panel which is lightweight and provided with a wide operating temperature and impact resistance.
The primary object can be achieved a touch panel made up of a first flat substrate having a first conductive layer on a lower main surface and a second flat substrate having a second conductive layer on an upper main surface, the first conductive layer and the second conductive layer facing each other with a certain space in between, the touch panel also including an undercoat material and a metal material being formed in one of the following arrangements A to E:
A. an undercoat layer is set between the first flat substrate and the first conductive layer, and a metal layer is set between the first flat substrate and the undercoat layer;
B. an undercoat layer is set between the second flat substrate and the second conductive layer, and a metal layer is set between the second flat substrate and the undercoat layer;
C. a first undercoat layer is set between the first flat substrate and the first conductive layer, a first metal layer is set between the first flat substrate and the first undercoat layer, a second undercoat layer is set between the second flat substrate an d the second conductive layer, and a second metal layer is set between the second flat substrate and the second undercoat layer;
D. a first undercoat layer is set between the first flat substrate and the first conductive layer, a metal layer is set between the first flat substrate and the first undercoat layer, and a second undercoat layer is set between the second flat substrate and the second conductive layer; and
E. a first undercoat layer is set between the first flat substrate and the first conductive layer, a second undercoat layer is set between the second flat substrate and the second conductive layer, and a metal layer is set between the second flat substrate and the second undercoat layer, wherein the undercoat material includes a metal oxide, and the metal material is a single metal element or an alloy of metal elements.
With this construction, the contact level between the undercoat layer and each flat substrate is improved, thereby preventing the conductive layer from being separated from the undercoat layer.
It is preferable to form the metal material from one or more of silicon, titanium, tin, and zinc.
The secondary object of the present invention can be achieved by a touch panel made up of a first flat substrate having a first conductive layer on a lower main surface and a second flat substrate having a second conductive layer on an upper main surface, the first and second conductive layers facing each other with a certain space in between, wherein the first flat substrate includes a conductive-layer forming member onto which the first conductive layer is formed and a supporting member which supports the conductive-layer forming member, wherein each of the second flat substrate and the conductive-layer forming member is formed from an amorphous polyolefine base resin sheet, wherein a difference between linear expansion coefficients of the supporting member and one of the second flat substrate and the conductive-layer forming member is within 1xc3x9710xe2x88x925/xc2x0 C.
By means of the excellent heat resistance of the amorphous polyolefine base resin sheet and an adjusted difference between the linear expansion coefficients of the layers, a wide operating temperature ranged from xe2x88x9240xc2x0 C. to 100xc2x0 C. can be provided for the touch panel. Also, the weight of the touch panel is reduced and impact resistance is increased by not using a glass substrate as used in a conventional case.
The supporting member can be formed from one of an amorphous polyolefine base resin sheet, a polycarbonate base sheet, and an acrylic resin sheet.
The amorphous polyolefine base resin sheet can be formed according to one of a solvent casting method and a fusion extruding method.
With this construction of the touch panel, the conductive layers each have a surface roughness that avoids the two conductive layers from sticking together, thereby preventing unreliable inputs from occurring when an input operation is repeated.
A protect member can be set on a lower main surface of the second flat substrate.
By means of this construction, durability to withstand input operations can be increased while the wide operating temperature is maintained.